Electrolyte and electrochemical device

ABSTRACT

An electrolyte including a dinitrile compound, a trinitrile compound, and propyl propionate. Based on the total weight of the electrolyte, the weight percentage of the dinitrile compound is X, the weight percentage of the trinitrile compound is Y, and the weight percentage of the propyl propionate is Z; where about 2 wt %≤(X+Y)≤about 11 wt %, about 0.1≤(X/Y)≤about 8, and about 0.01≤(Y/Z)≤about 0.3. The dinitrile compound comprises a compound of Formula (5): N—R2—(O—R3)n—O—R4—CN (5). The electrolyte is capable of effectively inhibiting the increase in DC internal resistance of an electrochemical device so that the electrochemical device has excellent cycle and storage performance.

CROSS REFERENCE TO THE RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 17/064,782, now U.S. Pat. No. 11,522,222, which isa continuation application of U.S. application Ser. No. 16/211,853, nowU.S. Pat. No. 10,833,363, where U.S. application Ser. No. 16/211,853claims the benefit of priority from China Patent Application No.201811108529.X, filed on 21 Sep. 2018, the disclosure of which is herebyincorporated by reference in its entirety.

1. TECHNICAL FIELD

The present disclosure relates to the technical field of energy storagetechnologies, in particular to an electrolyte and an electrochemicaldevice containing the electrolyte.

2. BACKGROUND

With the rapid development of electronic devices and electric vehicles,the requirement for high capacity electrochemical devices has grown. Inorder to increase capacity density of electrochemical devices, there isa need for effective methods to develop high-voltage electrochemicaldevices.

At present, electrochemical devices with a working voltage above 4.4Vhave become a hot research area in many research institutes andenterprises. However, at high voltages, the oxidation activity of thepositive electrode material increases, and the stability decreases,which makes the electrolyte decompose on the surface of the positiveelectrode easily or cause deterioration of the battery material,resulting in a decrease in battery capacity. In order to solve the aboveproblems, it is definitely necessary to provide an improvedelectrochemical device.

SUMMARY

An embodiment of the present application provides an electrolyte and anelectrochemical device containing the electrolyte, wherein theelectrolyte comprises a compound comprising two cyano groups (hereinalso referred to as “a dinitrile compound”), a compound comprising threecyano groups (herein also referred to as “a trinitrile compound”), andpropyl propionate. The dinitrile compound can form a protective film onthe cathode of the electrochemical device, so as to inhibit thedecomposition of the solvent in the electrochemical device. However,since the protective film itself is decomposed on the surface of thecathode at a high potential, the effect of inhibiting decomposition ofthe solvent cannot be sustained for a long time. The present inventorsunexpectedly found that by using a mixture of a dinitrile compound, atrinitrile compound and propyl propionate, a firm protective film whichis not easily decomposed on the surface of the cathode at a highpotential can be formed. The electrolyte according to the embodiment ofthe present application can effectively inhibit the increase in DCinternal resistance of the electrochemical device.

In an embodiment, the present application provides an electrolyte. Theelectrolyte comprises a dinitrile compound, a trinitrile compound, andpropyl propionate, wherein, based on the total weight of theelectrolyte, the weight percentage (X) of the dinitrile compound and theweight percentage (Y) of the trinitrile compound based on the totalweight of the electrolyte solution meet the conditions represented byFormula (1) and Formula (2):about 2 wt %≤(X+Y)≤about 11 wt %  (1); andabout 0.1≤(X/Y)≤about 8  (2).

According to an embodiment of the present application, the weightpercentage (Y) of the trinitrile compound and the weight percentage (Z)of the propyl propionate based on the total weight of the electrolytemeet the condition represented by Formula (3):about 0.01≤(Y/Z)≤about 0.3  (3).

According to an embodiment of the present application, the weightpercentage of the dinitrile compound is X, and X is about 0.01-10 wt %;the weight percentage of the trinitrile compound is Y, and Y is about0.01-10 wt %; and the weight percentage of the propyl propionate is Z,and Z is about 5-50 wt %. The electrolyte according to the embodimentsof the present application can effectively inhibit the increase in DCinternal resistance of the electrochemical device, thereby achieving abetter effect.

According to an embodiment of the present application, the electrolytefurther comprises a fluoroether, wherein based on the total weight ofthe electrolyte, the content of fluoroether is about 0.01-10 wt %. Thefluoroether can form a better protective film with the trinitrilecompound, thereby improving the DC internal resistance and the storageperformance of the electrochemical device.

According to an embodiment of the present application, the electrolytefurther comprises a cyclic phosphonic anhydride, wherein, based on thetotal weight of the electrolyte, the content of the cyclic phosphonicanhydride is about 0.01-10 wt %. The addition of the cyclic phosphonicanhydride can further inhibit the increase in DC internal resistanceduring the cycle.

According to an embodiment of the present application, the electrolytefurther comprises one selected from the group consisting of: a cycliccarbonate ester having a carbon-carbon double bond, a fluorinated chaincarbonate ester, a fluorinated cyclic carbonate ester, a compound havinga sulfur-oxygen double bond, and any combination thereof. Thesecompounds can form a firm protective film which is not easily to bedecomposed at the electrode interface with the dinitrile compound, thetrinitrile compound and propyl propionate, thereby further inhibitingthe side reactions in the electrochemical device and reducing thevoltage drop during storage of the electrochemical device, so as toimprove the long-term storage performance and reliability of theelectrochemical device.

In another embodiment, the present application provides anelectrochemical device and an electronic device using theelectrochemical device. The electrochemical device comprises electrodesand an electrolyte which is any of the electrolyte described above.

According to an embodiment of the present application, the electrodeincludes a current collector and a coating on the current collector. Thecoating includes a single-sided coating, a double-sided coating, or acombination thereof. The single-sided coating is a coating formed byapplying a slurry on one surface of the current collector. Thedouble-sided coating is a coating formed by applying a slurry on twosurfaces of the current collector. The electrode with the single-sidedcoating has an electrode compaction density D1, and the electrode withthe double-sided coating has an electrode compaction density D2, whereinD1 and D2 meet the following relationship: about 0.8≤D1/D2≤about 1.2.

According to an embodiment of the present application, the electrode sinclude a cathode and an anode In some embodiments, when the electrodeis an cathode, about 3.5 g/cm³≤D2≤about 4.3 g/cm³. In some otherembodiments, when the electrode is an anode, about 1.2 g/cm³≤D2≤1.8g/cm³.

In the electrochemical device according to the embodiments of thepresent application, when the electrolyte of the electrochemical devicecomprises a compound comprising two cyano groups, a compound comprisingthree cyano groups, and propyl propionate, and the electrode compactiondensities meet the above relationships, the electrode can have goodelectrical conductivity, the effects of the cathode and anode activematerials are well exerted, which is important to controlling theexpansion of electrochemical devices. Therefore, the electrochemicaldevice according to the embodiments of the present application achieveshigh capacity density and has excellent cycle and storage performances.

In another embodiment, the present application provides an electronicdevice including the electrochemical device.

Additional aspects and advantages of the embodiments of the presentapplication will be partially described, illustrated or explained by wayof examples in the description as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described according to the appended drawings inwhich:

The drawings needed for describing the embodiments of the presentapplication or the prior art will be briefly described below tofacilitate the description of the embodiments of the presentapplication. Obviously, the drawings in the following description areonly a portion of the embodiments of the present application. For thoseskilled in the art, the drawings of other embodiments can be obtainedaccording to the structures illustrated in the drawings without creativeefforts.

FIG. 1A shows the DC internal resistances of fresh batteries of ExamplesS1-1 and S1-2 of the present application and Comparative Example D1-1 atdifferent charge states (10% SOC, 20% SOC, and 70% SOC).

FIG. 1B shows the DC internal resistances of batteries of Examples S1-1and S1-2 of the present application and Comparative Example D1-1 atdifferent charge states (10% SOC, 20% SOC, and 70% SOC) after 200 cyclesof charge and discharge.

FIG. 1C shows the DC internal resistances of batteries of Examples S1-1and S1-2 of the present application and Comparative Example D1-1 atdifferent charge states (10% SOC, 20% SOC, and 70% SOC) after 400 cyclesof charge and discharge.

FIG. 2 is a view schematically showing the structure of an electrode Awith a single-sided coating of the present application.

FIG. 3 is a view schematically showing the structure of an electrode Bwith a double-sided coating of the present application.

FIG. 4 is a view schematically showing the structure of an electrode Cwith a single-sided coating and a double-sided coating of the presentapplication.

DETAILED DESCRIPTION

Embodiments of the present application will be described in detailbelow. Throughout the specification of the present application, the sameor similar components and components having the same or similarfunctions are denoted by similar reference numerals. The embodimentsdescribed herein with respect to the figures are explanatory, andillustrative, and are provided to facilitate the basic understanding ofthe application. The embodiments of the present application should notbe interpreted as limitations to the present application. Unlessotherwise expressly indicated, the following terms used herein have themeanings indicated below.

As used herein, the term “about” is used to describe and depict minorvariations. When used in connection with an event or circumstance, theterm may refer to an example in which the event or circumstance occursprecisely, and an example in which the event or circumstance occursapproximately. For example, when used in connection with a value, theterm may refer to a range of variation less than or equal to ±10% of thestated value, such as less than or equal to ±5%, less than or equal to±4%, less than or equal to ±3%, less than or equal to ±2%, less than orequal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%,or less than or equal to ±0.05%. In addition, amounts, ratios, and othervalues are sometimes presented in a range format in this application. Itis to be understood that such a range format is provided for convenienceand simplicity, and should be understood flexibly to include not onlythe numerical values that are explicitly defined in the range, but alsoall the individual values or sub-ranges that are included in the range,as if each value and sub-range are explicitly specified.

As used herein, “hydrocarbyl” covers alkyl, alkenyl, and alkynyl groups.For example, the hydrocarbyl may be a straight-chain hydrocarbonstructure having 1 to 20 carbon atoms. The hydrocarbon group also may bea branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms.When a hydrocarbon group having a specific number of carbon atoms isdefined, it may coverall geometric isomers having the carbon number. Thehydrocarbon group herein may also be a hydrocarbon group having 1 to 15carbon atoms, a hydrocarbon group having 1 to 10 carbon atoms, ahydrocarbon group having 1 to 5 carbon atoms, a hydrocarbon group having5 to 20 carbon atoms, a hydrocarbon group having 5 to 15 carbon atoms ora hydrocarbon group having 5 to 10 carbon atoms. Additionally, thehydrocarbon group may be optionally substituted. For example, thehydrocarbon group may be substituted by halo including fluorine,chlorine, bromine, and iodine, an alkyl group, an aryl group or aheteroaryl group.

As used herein, the “alkyl group” may be a linear saturated hydrocarbonstructure having 1 to 20 carbon atoms. The alkyl group also may be abranched or cyclic hydrocarbon structure having 3 to 20 carbon atoms.For example, the alkyl group may be an alkyl group having 1-20 carbonatoms, an alkyl group having 1-10 carbon atoms, an alkyl group having1-5 carbon atoms, an alkyl group having 5-20 carbon atoms, an alkylgroup having 5-15 carbon atoms, or alkyl group having 5-10 carbon atoms.When an alkyl group having a specific number of carbon atoms is defined,it may cover all geometric isomers having the carbon number. Therefore,for example, “butyl” means n-butyl, sec-butyl, isobutyl, tert-butyl andcyclobutyl; and “propyl” includes n-propyl, isopropyl and cyclopropyl.Examples of the alkyl group include, but are not limited to, methyl,ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, cyclobutyl, n-pentyl, isoamyl, neopentyl, cyclopentyl,methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl,n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornanyl and so on.Additionally, the alkyl group may be optionally substituted.

As used herein, the term “alkylene group” means a linear or brancheddivalent saturated hydrocarbon group. For example, the alkylene groupmay be an alkylene group having 1-20 carbon atoms, an alkylene grouphaving 1-15 carbon atoms, an alkylene group having 1-10 carbon atoms, analkylene group having 1-5 carbon atoms, an alkylene group having 5-20carbon atoms, an alkylene group having 5-15 carbon atoms, or alkylenegroup having 5-10 carbon atoms. Representative alkylene group includes(for example) methylene, ethane-1,2-diyl (“ethylene”), propane-1,2-diyl,propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl and the like.Additionally, the alkylene group may be optionally substituted.

As used herein, the term “alkenylene group” covers both linear andbranched alkenylene groups. When an alkenylene group having a specificnumber of carbon atoms is defined, it may cover all geometric isomershaving the carbon number. For example, the alkenylene group may be analkenylene group having 2-20 carbon atoms, an alkenylene group having2-15 carbon atoms, an alkenylene group having 2-10 carbon atoms, analkenylene group having 2-5 carbon atoms, an alkenylene group having5-20 carbon atoms, an alkenylene group having 5-15 carbon atoms, oralkenylene group having 5-10 carbon atoms. Representative alkenylenegroup includes (for example) ethenylene, propenylene, butenylene and thelike. Additionally, the alkenylene group may be optionally substituted.

As used herein, the term “aryl” encompasses both monocyclic andpolycyclic systems. A polycyclic ring may have two or more rings inwhich two carbons are shared by two adjacent rings (where the rings are“fused”), in which at least one of the rings is aromatic and other ringsmay be for example, a cycloalkyl group, a cycloalkenyl group, an arylgroup, a heterocyclyl group and/or a heteroaryl group. For example, thearyl group may be a C₆-C₅₀ aryl group, a C₆-C₄₀ aryl group, a C₆-C₃₀aryl group, a C₆-C₂₀ aryl group, or a C₆-C₁₀ aryl group. Representativearyl group includes (for example) phenyl, methylphenyl, propylphenyl,isopropylphenyl, benzyl and naphthalen-1-yl, naphthalen-2-yl and thelike. Additionally, the aryl group may be optionally substituted.

As used herein, the term “heteroaryl group” covers a monocyclicheteroaromatic group which may include one to three heteroatoms, forexample, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine, pyrimidine, and the like. Theterm heteroaryl group also includes a polycyclic heteroaromatic systemhaving two or more rings in which two atoms are shared by two adjacentrings (where the ring is “fused”), in which at least one of the rings isa heteroaryl group, and other rings may be a cycloalkyl group, acycloalkenyl group, an aryl group, a heterocyclyl group and/or aheteroaryl group. The heteroatom in the heteroaryl group may be forexample O, S, N, Se, and so on. For example, the heteroaryl group may bea C₂-C₅₀ heteroaryl group, a C₂-C₄₀ heteroaryl group, a C₂-C₁₀heteroaryl group, a C₂-C₂₀ heteroaryl group, or a C₂-C₁₀ heteroarylgroup. Additionally, the aryl group may be optionally substituted.

When the above substituents are substituted, the substituent is selectedfrom the group consisting of halogen, an alkyl group, a cycloalkylgroup, an alkenyl group, an aryl group, and a heteroaryl group.

As used herein, the content of each component is obtained based on thetotal weight of the electrolyte.

I. Electrolyte

An embodiment of the present application provides an electrolyte, whichcomprises an electrolyte and a solvent in which the electrolyte isdissolved. It is one of the main characteristics of the electrolyte ofthe present application that the electrolyte comprises a dinitrilecompound, a trinitrile compound, and propyl propionate, wherein, basedon the total weight of the electrolyte, the weight percentage of the isX and the weight percentage of the trinitrile compound is Y, and X and Ymeet the conditions represented by Formula (1) and Formula (2):about 2 wt %≤(X+Y)≤about 11 wt %  (1); andabout 0.1≤(X/Y)≤about 8  (2).

In some embodiments, X and Y meet about 2 wt %≤(X+Y)≤about 8 wt % andabout 0.1≤(X/Y)≤about 6 simultaneously. In some embodiments, X and Ymeet about 3 wt %≤(X+Y)≤6 wt % and about 0.2≤(X/Y)≤about 5simultaneously. In some embodiments, X and Y meet about 4 wt%≤(X+Y)≤about 5 wt % and about 0.3≤(X/Y)≤about 4 simultaneously. In someembodiments, X and Y meet about 2 wt %≤(X+Y)≤about 5 wt % and about0.1≤(X/Y)≤about 1 simultaneously.

In some embodiments, based on the total weight of the electrolyte, theweight percentage of the trinitrile compound is Y and the weightpercentage of the propyl propionate is Z, and Y and Z meet the conditionrepresented by Formula (3):about 0.01≤(Y/Z)≤about 0.3  (3).

In some embodiments, Y and Z meet about 0.01≤(Y/Z)≤about 0.2. In someembodiments, Y and Z meet about 0.02≤(Y/Z)≤about 0.1.

In some embodiments, the weight percentage of the dinitrile compound isabout 0.01-10 wt %. In some embodiments, the weight percentage of thedinitrile compound is not less than about 0.01 wt %, not less than about0.1 wt %, not less than about 0.3 wt %, or not less than about 0.5 wt %.In some embodiments, the weight percentage of the dinitrile compound isnot greater than about 10 wt %, not greater than about 8 wt %, or notgreater than about 6 wt %.

In some embodiments, the weight percentage of the trinitrile compound isabout 0.01-10 wt %. In some embodiments, the weight percentage of thetrinitrile compound is not less than about 0.01 wt %, not less thanabout 0.1 wt %, not less than about 0.3 wt %, or not less than about 0.5wt %. In some embodiments, the weight percentage of the trinitrilecompound is not greater than about 10 wt %, not greater than about 8 wt%, not greater than about 5 wt %, not greater than about 4 wt %, or notgreater than about 3 wt %.

In some embodiments, the weight percentage of the propyl propionate isabout 5-50 wt %. In some embodiments, the weight percentage (Z) of thepropyl propionate is about 5-40 wt %, about 10-40 wt %, about 10-30 wt%, about 20-50 wt %, about 20-40 wt %, about 20-30 wt %, or about 25-30wt %.

Compound Comprising Two Cyano Groups (Dinitrile Compound)

In some embodiments, the dinitrile compound according to the presentapplication includes a compound of Formula [4] or [5]:CN—R₁—CN  [4],CN—R₂—(O—R₃)_(n)—O—R₄—CN  [5],

or a combination thereof,

wherein in Formula [4] or [5], R₁, R₂, R₃ and R₄ are each independentlyan alkylene having 1-20 carbon atoms, for example, an alkylene grouphaving 1-15 carbon atoms, an alkylene group having 1-10 carbon atoms, analkylene group having 1-5 carbon atoms, an alkylene group having 5-10carbon atoms, an alkylene group having 5-20 carbon atoms, an alkylenegroup having 5-15 carbon atoms, an alkenylene group having 2-20 carbonatoms, an alkenylene group having 2-15 carbon atoms, an alkenylene grouphaving 2-10 carbon atoms, an alkenylene group having 2-5 carbon atoms,an alkenylene group having 5-20 carbon atoms, an alkenylene group having5-15 carbon atoms, or an alkenylene group having 5-10 carbon atoms, andn is an integer from 0 to 5.

In some embodiments, the dinitrile compound according to the presentapplication is a compound of Formula [4] or [5].

In some embodiments, the dinitrile compound of the present applicationincludes, but is not limited to, butanedinitrile, glutaronitrile,adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane,1,8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane,1,12-dicyanododecane, tetramethylbutanedinitrile,2-methylglutaronitrile, 2,4-dimethylglutaronitrile,2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane,2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane,1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene,1,4-dicyanobenzene, 3,5-dioxa-pimelonitrile, 1,4-bis(cyanoethoxy)butane,ethylene glycol bis(2-cyanoethyl)ether, diethylene glycolbis(2-cyanoethyl)ether, triethylene glycol bis(2-cyanoethyl)ether,tetraethylene glycol bis(2-cyanoethyl)ether,3,6,9,12,15,18-hexaoxaeicosanoic dinitrile,1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane,1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl)ether,1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene,1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene,1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene,1,6-dicyano-2-methyl-3-hexene, or1,6-dicyano-2-methyl-5-methyl-3-hexene. The dinitrile compounds may beused alone or in combination of two or more thereof.

Compound Comprising Three Cyano Groups (Trinitrile Compound)

In some embodiments, the trinitrile compound according to the presentapplication includes a compound of Formula [6] or [7]:

or a combination thereof,

wherein in Formula [6], x, y, and z represents an integer from 0 to 5and x, y, and z are not 0 at the same time; and

in Formula [7], R₅ may be hydrogen or an alkyl group having 1-20 carbonatoms, for example, an alkyl group having 1-10 carbon atoms, an alkylgroup having 1-5 carbon atoms, an alkyl group having 5-20 carbon atoms,an alkyl group having 5-15 carbon atoms, or an alkyl group having 5-10carbon atoms; R₆, R₇, and R₈ each independently may be an alkylene grouphaving 1-20 carbon atoms, for example, an alkylene group having 1-15carbon atoms, an alkylene group having 1-10 carbon atoms, an alkylenegroup having 1-5 carbon atoms, an alkylene group having 5-20 carbonatoms, an alkylene group having 5-15 carbon atoms, or an alkylene grouphaving 5-10 carbon atoms; and X₄, X₅ and X₆ each independently may be—R₉—CN, wherein R₉ may be an alkylene group having 1-20 carbon atoms,for example, an alkylene group having 1-15 carbon atoms, an alkylenegroup having 1-10 carbon atoms, an alkylene group having 1-5 carbonatoms, an alkylene group having 5-20 carbon atoms, an alkylene grouphaving 5-15 carbon atoms, or an alkylene group having 5-10 carbon atoms.

In some embodiments, the trinitrile compound according to the presentapplication is a compound of Formula [6] or [7].

In some embodiments, the trinitrile compound of the present applicationincludes, but is not limited to, 1,3,5-pentanetricarbonitrile,1,2,3-propanetrinitrile, 1,3,6-hexanetricarbonitrile,1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane,1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane,1,1,1-tris(cyanoethoxymethylene)propane,3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane,1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane. Thetrinitrile compounds may be used alone or in combination of two or morethereof.

Fluoroether Compound

In some embodiments, the fluoroether compound of the present applicationincludes at least one of the compounds of Formula [8], Formula [9],Formula [10], or Formula [11]:Rf1-O—Rf2  [8];Rf1-O—R  [9];Rf1-O—(R′—O)_(n)—Rf2  [10]; andRf1-O—(R′—O)_(n)—R  [11],

where in Formulae [8], [9], [10], and [11], Rf1 and Rf2 are eachindependently a linear or branched C₁ to C₁₂ fluoroalkyl group at leastone hydrogen atom of which is replaced with fluorine, R is a linear orbranched C₁ to C₁₂ alkyl group, and R′ is a linear or branched C₁ to C₅alkylene group, and n is an integer from 1 to 5.

In some embodiments, the fluoroether compound of the present applicationis a compound of Formula [8], Formula [9]. Formula [10], or Formula[11].

In some embodiments, Rf1 or Rf2 is each independently a fluoroalkylgroup selected from the group consisting of HCF₂—, CF₃—, HCF₂CF₂—,CH₃CF₂—, CF₃CH₂—, CF₃CF₂—, (CF₃)₂CH—, HCF₂CF₂CH₂—, CF₃CH₂CH₂—,HCF₂CF₂CF₂CH₂—, HCF₂CF₂CF₂CF₂CH₂—, CF₃CF₂CH₂—, CF₃CFHCF₂CH₂—,HCF₂CF(CF₃)CH₂—, and CF₃CF₂CH₂CH₂—.

The fluoroether can form a better protective film with the trinitrilecompound, thereby further improving the DC internal resistance and thestorage performance of the battery.

In some embodiments, the fluoroether of the present applicationincludes, but is not limited to:

HCF₂CF₂CH₂OCF₂CF₂H(FEPE), (CF₃)₂CFCF(CF₂CF₃)(OCH₃) (TMMP),CF₃CHFCF₂CH(CH₃)OCF₂CHFCF₃(TPTP), HCF₂CF₂CH₂OCF₂CF₂CF₂CF₂H,HCF₂CF₂OCH₂CF₃, HCF₂CF₂OCH₂CH₂OCF₂CF₂H, HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂H,HCF₂CF₂CH₂OCF₂CF₂CF₂H, HCF₂CF₂OCH₂CH₂OCF₂CF₂CF₂H,HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂H, CH₃OCH₂CH₂OCH₂CH₂F, CH₃OCH₂CH₂OCH₂CF₃,CH₃OCH₂CH(CH₃)OCH₂CH₂F, CH₃OCH₂CH(CH₃)OCH₂CF₃, FCH₂CH₂OCH₂CH₂OCH₂CH₂F,FCH₂CH₂OCH₂CH(CH₃)OCH₂CH₂F, CF₃CH₂O(CH₂CH₂O)₂CH₂CF₃ orCF₃CH₂OCH₂CH(CH₃)OCH₂CF₃. The fluoroether may be used alone or incombination of two or more thereof.

The structural formulas of FEPE, TMMP, and TPTP are shown below:

In some embodiments, based on the total weight of the electrolyte, thecontent of the fluoroether is not less than about 0.01 wt %, not lessthan about 0.1 wt %, or not less than about 0.5 wt %. In someembodiments, the content of the fluoroether is not greater than about 5wt %, not greater than about 4 wt %, not greater than about 3 wt %, ornot greater than about 2 wt %.

Cyclic Phosphonic Anhydride Compound

In some embodiments, the cyclic phosphonic anhydride according to thepresent application includes one or more of the compounds of Formula[12]:

wherein in Formula [12], R₁₀, R₁₁, and R₁₂ each independently may behydrogen; each independently may be an alkyl group having 1-20 carbonatoms, for example, an alkyl group having 1-15 carbon atoms, an alkylgroup having 1-10 carbon atoms, an alkyl group having 1-5 carbon atoms,an alkyl group having 5-20 carbon atoms, an alkyl group having 5-15carbon atoms, and an alkyl group having 5-10 carbon atoms; and eachindependently may be an aryl group having 6-50 carbon atoms, forexample, an aryl group having 6-30 carbon atoms, an aryl group having6-26 carbon atoms, an aryl group having 6-20 carbon atoms, an aryl grouphaving 10-50 carbon atoms, an aryl group having 10-30 carbon atoms, anaryl group having 10-26 carbon atoms, or an aryl group having 10-20carbon atoms, wherein R₁₀, R₁₁, and R₁₂ may be different from or thesame as each other, or any two of them are the same.

In some embodiments, the cyclic phosphonic anhydride compound of thepresent application includes, but is not limited to, compounds offollowing formulae, which may be used alone, or in combination of two ormore thereof:

In some embodiments, based on the total weight of the electrolyte, thecontent of the cyclic phosphonic anhydride is not less than about 0.01wt % or not less than about 0.1 wt %. In some embodiments, the contentof the cyclic phosphonic anhydride is not less than about 0.3 wt % ornot less than about 0.5 wt %. In some embodiments, the content of thecyclic phosphonic anhydride is not greater than about 4 wt % or notgreater than about 3 wt %.

Other Additives

The electrolyte of the present application may further comprises one ormore selected from the group consisting of: a cyclic carbonate esterhaving a carbon-carbon double bond, a fluoro chain carbonate ester, afluorinated cyclic carbonate ester, or a compound having a sulfur-oxygendouble bond.

In some embodiments, the cyclic carbonate ester having a carbon-carbondouble bond useful in the present application includes, but is notlimited to: vinylene carbonate, methyl vinylene carbonate, ethylvinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethylvinylene carbonate, fluorovinylene carbonate, andtrifluoromethylvinylene carbonate; vinyl ethylene carbonate,1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate,1-n-propyl-2-vinylethylene carbonate, 1-methyl-2-vinylethylenecarbonate, 1,1-divinylethylene carbonate, and 1,2-divinylethylenecarbonate; and 1,1-dimethyl-2-methylene ethylene carbonate, and1,1-diethyl-2-methylene ethylene carbonate. The cyclic carbonate esterhaving a carbon-carbon double bond may be used alone or in combinationof two or more thereof.

In some embodiments, based on the total weight of the electrolyte, thecontent of the cyclic carbonate ester having a carbon-carbon double bondis not less than about 0.01 wt %, not less than about 0.1 wt %, or notless than about 0.3 wt %. In some embodiments, the content of the cycliccarbonate ester having a carbon-carbon double bond is not less thanabout 0.5 wt %. In some embodiments, the content of the cyclic carbonateester having a carbon-carbon double bond is not greater than about 5 wt%, not greater than about 3 wt %, or not greater than about 1 wt %.

In some embodiments, the fluorinated chain carbonate ester according tothe present application includes, but is not limited to: fluoromethmetylcarbonate, difluoromethmethyl carbonate, trifluoromethmethyl carbonate,trifluoroethmethyl carbonate, or bis(trifluoroethyl) carbonate. Thefluorinated chain carbonate ester may be used alone or in combination oftwo or more thereof.

In some embodiments, based on the total weight of the electrolyte, thecontent of the fluorinated chain carbonate ester is not less than about0.01 wt % or not less than about 0.1 wt %. In some embodiments, thecontent of the fluorinated chain carbonate ester is not less than about0.3 wt %. In some embodiments, the content of the fluorinated chaincarbonate ester is not less than about 0.5 wt %. In some otherembodiments, the content of the fluorinated chain carbonate ester is notgreater than about 3 wt % or not greater than about 5 wt %. In someother embodiments, the content of the fluorinated chain carbonate esteris not greater than about 1 wt %. In some embodiments, the fluorinatedcyclic carbonate ester according to the present application includes,but is not limited to, fluoroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylenecarbonate, 4,5-difluoro-4-methylethylene carbonate,4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylenecarbonate, 4-(fluoromethyl)-ethylene carbonate,4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylenecarbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate,4,5-difluoro-4,5-dimethylethylene carbonate, and4,4-difluoro-5,5-dimethylethylene carbonate. The fluorinated cycliccarbonate esters may be used alone or in combination of two or morethereof.

In some embodiments, the content of the fluorinated cyclic carbonateester is not less than about 0.1 wt % based on the total weight of theelectrolyte. In some embodiments, the content of the fluoro cycliccarbonate ester is not less than about 0.5 wt %. In some embodiments,the content of the fluorinated cyclic carbonate ester is not less thanabout 2 wt %. In some embodiments, the content of the fluorinated cycliccarbonate ester is not less than about 4 wt %. In some embodiments, thecontent of the fluorinated cyclic carbonate ester is not greater thanabout 15 wt %. In some embodiments, the content of the fluorinatedcyclic carbonate ester is not greater than about 10 wt %. In someembodiments, the content of the fluorinated cyclic carbonate ester isnot greater than about 8 wt %.

In some embodiments, the compound having a sulfur-oxygen double bondaccording to the present application includes, but is not limited to: acyclic sulfate ester, a chain sulfate ester, a chain sulfonate ester, acyclic sulfonate ester, a chain sulfite ester, a cyclic sulfite ester, achain sulfone, a cyclic sulfones, and so on. The compound having asulfur-oxygen double bond may be used alone or in combination of two ormore thereof.

In some embodiments, based on the total weight of the electrolyte, thecontent of the compound having a sulfur-oxygen double bond is not lessthan about 0.01 wt %. In some embodiments, the content of the compoundhaving a sulfur-oxygen double bond is not less than about 0.1 wt %. Insome embodiments, the content of the compound having a sulfur-oxygendouble bond is not less than about 0.3 wt %. In some embodiments, thecontent of the compound having a sulfur-oxygen double bond is not lessthan about 0.5 wt %. In some other embodiments, the content of thecompound having a sulfur-oxygen double bond is not greater than about 5wt %. In some embodiments, the content of the compound having asulfur-oxygen double bond is not greater than about 4 wt %. In someembodiments, the content of the compound having a sulfur-oxygen doublebond is not greater than about 3 wt %.

In some embodiments, the cyclic sulfate ester according to the presentapplication includes, but is not limited to: 1,2-ethylene glycolsulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate,1,2-butylene glycol sulfate, 1,3-butylene glycol sulfate, 1,4-butyleneglycol sulfate, 1,2-pentylene glycol sulfate, 1,3-pentylene glycolsulfate, 1,4-pentylene glycol sulfate, and 1,5-pentylene glycol sulfate.The cyclic sulfate ester may be used alone or in combination of two ormore thereof.

In some embodiments, the chain sulfate ester according to the presentapplication includes, but is not limited to: a dialkyl sulfate such asdimethyl sulfate, methyl ethyl sulfate, and diethyl sulfate. The chainsulfate ester may be used alone or in combination of two or morethereof.

In some embodiments, the chain sulfonate ester according to the presentapplication includes, but is not limited to: methyl fluorosulfonate,ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate,butyl dimesylate, methyl 2-(methylsulfonyloxy)propionate, ethyl2-(methylsulfonyloxy)propionate, methyl methylsulfonyloxyacetate, ethylmethylsulfonyloxyacetate, phenyl methylsulfonate, and pentafluorophenylmethylsulfonate. The chain sulfonate ester may be used alone or incombination of two or more thereof.

In some embodiments, the cyclic sulfonate ester according to the presentapplication includes, but is not limited to: 1,3-propanesultone,1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone,3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone,2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone,1-propene-1,3-sultone, 2-propene-1,3-sultone,I-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone,3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone,2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone,1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone,3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone,2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone,1,4-butane sultone, 1,5-pentane sultone, methylene methanedisulfonate,and ethylene methanedisulfonate. The cyclic sulfonate ester may be usedalone or in combination of two or more thereof.

In some embodiments, the chain sulfite ester according to the presentapplication includes, but is not limited to: dimethyl sulfite, methylethyl sulfite, and diethyl sulfite. The chain sulfite ester may be usedalone or in combination of two or more thereof.

In some embodiments, the cyclic sulfite ester according to the presentapplication includes, but is not limited to: 1,2-ethylene glycolsulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite,1,2-butylene glycol sulfite, 1,3-butylene glycol sulfite, 1,4-butyleneglycol sulfite, 1,2-pentylene glycol sulfite, 1,3-pentylene glycolsulfite, 1,4-pentylene glycol sulfite, and 1,5-pentylene glycol sulfite.The cyclic sulfite ester may be used alone or in combination of two ormore thereof.

In some embodiments, the chain sulfone ester according to the presentapplication includes, but is not limited to: a dialkyl sulfone compoundsuch as dimethyl sulfone, and diethyl sulfone.

In some embodiments, the cyclic sulfone according to the presentapplication includes, but is not limited to: sulfolane, methylsulfolane, 4,5-dimethyl sulfolane, and sulfolene. The cyclic sulfone maybe used alone or in combination of two or more thereof.

Electrolyte

The electrolyte used in the electrolyte according to the embodiments ofthe present application may be an electrolyte known in the prior art,including, but not limited to: an inorganic lithium salt, for exampleLiClO₄, LiAsF₆, LiPF₆, LiBF₄, LiSbF₆, LiSO₃F, and LiN(FSO₂)₂; afluorine-containing organic lithium salt, for example LiCF₃SO₃,LiN(FSO₂)(CF₃SO₂), LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, cyclic lithium1,3-hexafluoropropane disulfonimide, cyclic lithium1,2-tetrafluoroethane disulfonimide, LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃,LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂, LiPF₄(CF₃SO₂)₂, LiPF₄(C₂F₅SO₂)₂, LiBF₂(CF₃)₂,LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂, and LiBF₂(C₂F₅SO₂)₂; and a lithium saltcontaining a dicarboxylic acid complex, for example, lithiumbis(oxalato)borate, lithium difluoro(oxalato)borate, lithiumtris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, andlithiumtetrafluoro(oxalato)phosphate. In addition, the electrolyte maybe used alone or in combination of two or more thereof. For example, insome embodiments, the electrolyte includes a combination of LiPF₆ andLiBF₄. In some embodiments, the electrolyte includes a combination of aninorganic lithium salt such as LiPF₆ or LiBF₄ and a fluorine-containingorganic lithium salt such as LiCF₃SO₃, LiN(CF₃SO₂)₂, or LiN(C₂F₅SO₂)₂.In some embodiments, the concentration of the electrolyte is in therange of about 0.8-about 3 mol/L, for example, about 0.8-about 2.5mol/L, about 0.8-about 2 mol/L, about 1-about 2 mol/L, for example, 1mol/L, 1.15 mol/L, 1.2 mol/L, 1.5 mol/L, 2 mol/L or 2.5 mol/L.

Solvent

The solvent used in the electrolyte according to the embodiments of thepresent application may be any non-aqueous solvent known in the art as asolvent for an electrolyte.

In some embodiments, the non-aqueous solvent useful in the presentapplication includes, but is not limited to: a cyclic carbonate ester, achain carbonate ester, a cyclic carboxylate ester, a chain carboxylateester, a cyclic ether, a chain ether, a phosphorus-containing organicsolvent, a sulfur-containing organic solvent, an aromaticfluorine-containing solvent or any combination thereof.

In some embodiments, the cyclic carbonate ester according to the presentapplication generally has 3-6 carbon atoms, and includes, but is notlimited to: for example, ethylene carbonate, propylene carbonate,butylene carbonate, and other cyclic carbonates.

In some embodiments, the chain carbonate ester according to the presentapplication includes, but is not limited to: a chain carbonate estersuch as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate,methyl n-propyl carbonate, ethyl n-propyl carbonate, and di-n-propylcarbonate; and a fluorinated chain carbonate ester, for example,bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate,bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate,bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate,2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and2,2,2-trifluoroethylmethyl carbonate.

In some embodiments, the cyclic carboxylate ester according to presentapplication includes, but is not limited to: γ-butyrolactone,γ-valerolactone, and the like, and a cyclic carboxylate ester somehydrogen atoms of which are substituted with fluorine.

In some embodiments, the chain carboxylate ester according to thepresent application includes, but is not limited to: methyl acetate,ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate,sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methylpropionate, ethyl propionate, propyl propionate, isopropyl propionate,methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate,ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate andethyl pivalate or the like, and a chain carboxylate ester some hydrogenatoms of which are substituted with fluorine. The fluorinated chaincarboxylate ester includes, but is not limited to: methyltrifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyltrifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate.

In some embodiments, the cyclic ether according to the presentapplication includes, but is not limited to: tetrahydrofuran,2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane,4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane and dimethoxypropane.In some embodiments, the chain ether according to the presentapplication includes, but is not limited to: dimethoxymethane,1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane,1,1-diethoxyethane, 1,2-di ethoxyethane, ethoxymethoxymethane,1,1-ethoxymethoxyethane and 1,2-ethoxymethoxyethane.

In some embodiments, the phosphorus-containing organic solvent accordingto the present application includes, but is not limited to: trimethylphosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethylphosphate, ethylene methyl phosphate, ethylene ethyl phosphate,triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenylphosphite, tris(2,2,2-trifluoroethyl) phosphate andtris(2,2,3,3,3-pentafluoropropyl) phosphate.

In some embodiments, the sulfur-containing organic solvent according tothe present application includes, but is not limited to: sulfolane,2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone,ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methylmethanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethylethanesulfonate, dimethyl sulfate, diethyl sulfate and dibutyl sulfate,as well as a sulfur-containing organic solvent some hydrogen atoms ofwhich are substituted with fluorine.

In some embodiments, the aromatic fluorine-containing organic solventaccording to the present application includes, but is not limited to:fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene,pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

In some embodiments, the non-aqueous solvent of the present applicationmay be used alone, or in combination of two or more thereof:

II. Electrochemical Device

The electrochemical device of the present invention includes any devicein which an electrochemical reaction takes place, and specific examplesinclude all kinds of primary batteries, secondary batteries, fuel cells,solar cells, or capacitors. In particular, the electrochemical device isa lithium secondary battery including a lithium metal secondary battery,a lithium ion secondary battery, a lithium polymer secondary battery ora lithium ion polymer secondary battery. In some embodiments, theelectrochemical device of the present application is an electrochemicaldevice having a cathode having a cathode active material capable ofabsorbing and releasing metal ions; an anode having a anode activematerial capable of absorbing and releasing metal ions, andcharacterized by comprising any of the electrolytes of the presentapplication.

Electrolyte

The electrolyte used in the electrochemical device of the presentapplication is any of the aforementioned electrolytes according to thepresent application. Moreover, the electrolyte used in theelectrochemical device of the present application may include otherelectrolytes falling within the scope of present application.

Anode

The anode material used in the electrochemical device according to theembodiments of the present application can be prepared using materials,construction and manufacturing methods well known in the art. Forexample, the anode of the present application can be prepared using thetechnique described in U.S. Pat. No. 9,812,739B, the entire contents ofwhich are incorporated herein by reference.

In some embodiments, the anode active material is any substance capableof electrochemically absorbing and releasing a metal ion such as lithiumion. In some embodiments, the anode active material includes acarbonaceous material, a silicon-carbon material, an alloy material or alithium-containing metal composite oxide material. In some embodiments,the anode active material includes one or more of those described above.

In some embodiments, the anode can be formed by adding a binder and asolvent to, and if necessary, adding a thickener, a conductive material,a filler, or the like the anode active material, to prepare a slurry,coating the slurry to a current collector, drying, and then pressing.

In some embodiments, when the anode includes an alloy-based material, athin film layer (anode active material layer) as an anode activematerial can be formed by vapor deposition, sputtering, or plating.

In some embodiments, when the anode includes lithium metal, an anodeactive material layer is formed from, for example, a conductive skeletonof twisted spherical shape and metal particles dispersed in theconductive skeleton, wherein the conductive skeleton of twistedspherical shape may have a porosity of about 5% to about 85%, and aprotective layer may be further disposed on the anode active materiallayer of lithium metal.

Cathode

The cathode material used in the electrochemical device of the presentapplication can be prepared using materials, construction andmanufacturing methods well known in the art. In some embodiments, thecathode of the present application can be prepared using the techniquedescribed in U.S. Pat. No. 9,812,739B, the entire contents of which areincorporated herein by reference.

In some embodiments, the cathode active material includes, but is notlimited to: a sulfide, a phosphate salt compound and alithium-transition metal composite oxide. In some embodiments, thecathode active material includes a lithium-transition metal compoundwhich has a structure capable of removing and intercalating lithiumions. In some embodiments, the composition of the lithium-transitionmetal compound can refer to the technical content described in U.S. Pat.No. 9,812,739B.

In some embodiments, the cathode is prepared by forming a cathodematerial from a cathode active material layer including alithium-transition metal compound powder and a binder on a currentcollector.

In some embodiments, the cathode active material layer can generally beproduced by: dry mixing a cathode material and a binder (and aconductive material and a thickener, if necessary) to form flakes,pressing the obtained flakes on a cathode current collector ordissolving or dispersing the material in a liquid medium to form aslurry, coating the slurry on a cathode current collector, and drying.In some embodiments, the material of the cathode active material layerincludes any material known in the art. In some embodiments, the cathodeactive material layer includes materials described in U.S. Pat. No.9,812,739B.

Electrode Compaction Density

The electrochemical device of the present application comprises acathode and an anode, a separator and an electrolyte. The electrodeincludes a current collector and a coating on the current collector. Thecoating includes a single-sided coating, a double-sided coating, or acombination thereof. The single-sided coating is a coating formed byapplying a slurry on one surface of the current collector. Thedouble-sided coating is a coating formed by applying a slurry on twoopposite surfaces of the current collector.

In some embodiments, as shown in FIG. 2 , an electrode A includes acurrent collector 1 and a coating 2 on the current collector 1. As shownin FIG. 2 , the coating 2 is only present on one surface of the currentcollector, and such coating is a single-sided coating.

In some embodiments, as shown in FIG. 3 , an electrode B includes acurrent collector 1 and a coating 2 on the current collector. As shownin FIG. 3 , the coating 2 is present on two opposite surfaces of thecurrent collector, and such coating is a double-sided coating.

In some embodiments, as shown by an electrode C in FIG. 4 , one surfaceof a portion of a current collector 1 is coated with a slurry to form acoating 2 and the two opposite surfaces of the other portion of thecurrent collector 1 are coated with a slurry to form a coating 2. Suchcoating includes both a single-sided coating and a double-sided coating.

In a wound electrochemical device, the cathode and the cathode areusually each formed by winding an elongated electrode, so that both asingle-sided coating and a double-sided coating are present on theelongated electrode. In a laminated electrochemical device, the cathodeand the anode are usually formed by laminating-shaped electrodes, andthere is only a single-sided coating or a double-sided coating on thesame electrode. In an electrochemical device in which the wound andlaminated electrode s are assembled in combination, the cathode andanode generally comprise an elongated electrode having both asingle-sided coating and a double-sided coating, and a-shaped electrodehaving only a single-sided coating or a double-sided coating.

The electrode has an electrode compaction density. The electrodecompaction density is obtained by: measuring the thickness of anelectrode using a precise measurement tool, such as a ten-thousandthsmicrometer; then taking the electrode of a certain area and accuratelymeasuring the area and weight; and calculating the electrode compactiondensity by a formula below:Electrode compaction density=(Weight of electrode−Weight of currentcollector)/Area of electrode/(Thickness of electrode−Thickness ofcurrent collector)

A lower compaction density makes the porosity higher, making some of theparticles in an insulating state, and unable to participate in chargeand discharge, thereby resulting in a low specific discharge capacity,thus affecting the performance of the electrochemical device. A too highcompaction density may cause difficulty in infiltrability of theelectrolyte and decrease in solution retention, such that the cycle andrate performances cannot be guaranteed. Properly controlling theelectrodecompaction density of the single-sided and double-sided coatingis important to obtain electrochemical devices with high capacitydensity, and excellent cycle and storage performances.

In some embodiments, the electrode with a single-sided coating has anelectrode compaction density D1, and an electrode with a double-sidedcoating has an electrode compaction density D2, and D1 and D2 meet therelationship: about 0.8≤D1/D2≤about 1.2, under this circumstance, theeffects of the cathode and anode active materials are well exerted, sothat the electrode can obtain good electrical conductivity, which isalso important to control the expansion of electrochemical devices.Therefore, the obtained electrochemical device has high capacity densityand excellent cycle and storage performances.

In some embodiments, D1 and D2 meet the relationship: about0.9≤D1/D2≤about 1.1. Under this circumstance, the performance of theelectrochemical device can be further improved.

In some embodiments, D1 and D2 meet the relationship: about0.9≤D1/D2≤about 1.1.

In some embodiments, D1 and D2 meet the relationship: about0.95≤D1/D2≤about 1.05. Under this circumstance, the distributions ofpores and pore sizes in the single-sided coating and the double-sidedcoating are more uniform, the distributions of the conductive agent andthe binder are more uniform, the contact resistance and charge exchangeresistance of the electrode are lowered, and the active area capable ofparticipating in the reaction is increased, thereby significantlyimproving the electrochemical performance of the material and furtherimproving the performances of the electrochemical device.

In some embodiments, the electrode may be a cathode or an anode. Whenthe electrode is a cathode, about 3.5 g/cm³≤D2≤about 4.3 g/cm³. When D2is within this range, the cathode can have good electrical conductivity,and the effect of the cathode active material can be well exerted. Whenthe electrode is an anode, about 1.2 g/cm³≤D2≤about 1.8 g/cm³. When D2is within this range, the anode can have a higher breaking strength,thereby preventing the electrode particles from falling off during thecycle.

Separator

In some embodiments, the electrochemical device of the presentapplication is provided with a separator between the positive electrodeand the negative electrode to prevent short circuit. The material andshape of the separator used in the electrochemical device of the presentapplication are not particularly limited, and may be any of thetechniques disclosed in the prior art. In some embodiments, theseparator includes a polymer or an inorganic substance or the likeformed from a material which is stable to the electrolyte of the presentapplication.

For example, the separator may include a substrate layer and a surfacetreatment layer. The substrate layer is a non-woven fabric, film, orcomposite film having a porous structure, and the material of thesubstrate layer is at least one selected from polyethylene,polypropylene, polyethylene terephthalate, and polyimide. Particularly,a porous polypropylene film, a porous polyethylene film, a polypropylenenonwoven fabric, a polyethylene nonwoven fabric, or a porouspolypropylene-polyethylene-polypropylene composite film may be used.

At least one surface of the substrate layer is provided with a surfacetreatment layer, which may be a polymer layer or an inorganic layer, ora layer formed by mixing a polymer and an inorganic substance.

The inorganic layer comprises inorganic particles and a binder. Theinorganic particles are one or more selected from alumina, silica,magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide,nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, siliconcarbide, boehmite, aluminum hydroxide, magnesium hydroxide, calciumhydroxide and barium sulfate. The binder is one or more selected frompolyvinylidene fluoride, a copolymer of vinylidenefluoride-hexafluoropropylene, a polyamide, polyacrylonitrile, apolyacrylate ester, polyacrylic acid, a polyacrylate salt,polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate,polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layercontains a polymer, and the material of the polymer includes at leastone of a polyamide, polyacrylonitrile, a polyacrylate ester, polyacrylicacid, a polyacrylate salt, polyvinylpyrrolidone, polyvinyl ether,polyvinylidene fluoride or poly(vinylidenefluoride-hexafluoropropylene).

III. Application

At a high voltage, the oxidizability of the cathode material isincreased, and the stability is lowered, which makes the electrolyteeasily decompose on the surface of the positive electrode or results indeterioration of the materials of the electrochemical device, so thatthe capacity of the electrochemical device is decreased. Prior to thepresent application, the primary solution is to add a film-formingadditive to the electrolyte. However, doing so will cause an increase inthe DC internal resistance of the battery, thereby resulting in adecrease in the cycle performance and a decrease in the capacityretention rate.

The electrolyte according to the embodiments of the present applicationcan be used to inhibit the increase in DC internal resistance of anelectrochemical device, and thus applicable to an electronic devicecomprising the electrochemical device.

The use of the electrochemical device according to the presentapplication is not particularly limited, and can be used in variousknown applications, such as notebook computers, pen-input computers,mobile computers, e-book players, portable phones, portable faxmachines, portable copiers, portable printers, head-mounted stereoheadphones, video recorders, LCD TVs, portable cleaners, portable CDplayers, Mini discs, transceivers, electronic notebooks, calculators,memory cards, portable recorders, radios, backup power sources, motors,vehicles, motorcycles, motorbicycle, bicycles, lighting apparatus, toys,game consoles, clocks, electric tools, flashing light, cameras, largebatteries for household use, or lithium ion capacitors.

EXAMPLES

Hereinafter, the present application will be specifically described byway of examples and comparative examples; however, the presentapplication is not limited thereto as long as they do not deviate fromthe spirit of the present application.

1. Preparation of Lithium-Ion Battery

(1) Preparation of an Anode

Graphite, conductive carbon black (Super-P), styrene-butadiene rubber,and sodium carboxymethyl cellulose (CMC) were mixed at a weight ratio ofabout 95:2:2:1 in deionized water as a solvent, and stirred uniformly,to obtain an anode slurry. The slurry was coated on a copper foil havinga thickness of about 12 μm, dried, cold pressed, and cut, and then a tabwas welded, to obtain an anode.

(2) Preparation of a Cathode

Lithium cobalt oxide (LiCoO₂), conductive carbon black (Super-P), andpolyvinylidene fluoride (PVDF) were mixed at a weight ratio of about95:2:3 in N-methylpyrrolidone as a solvent, and stirred uniformly, toobtain a cathode slurry. The slurry was coated on an aluminum foilhaving a thickness of about 12 μm, dried, cold pressed, and cut, andthen a tab was welded, to obtain a cathode.

(3) Preparation of an Electrolyte:

Under a dry argon atmosphere, EC, PC, and DEC (at a weight ratio ofabout 1:1:1) were mixed, and then LiPF₆ was added and mixed uniformly,to form a basic electrolyte, in which the concentration of LiPF₆ is 1.15mol/L. Different amounts of substances shown in Tables 1-1 to 9 wereadded to the basic electrolyte to obtain the electrolytes of differentexamples and comparative examples, wherein the contents of eachsubstance in the electrolyte described below were obtained based on thetotal weight of the electrolyte.

(4) Preparation of a Separator

A porous PE polymer film was used as a separator.

(5) Preparation of Lithium-Ion Battery

The obtained cathode, anode and separator were wound in sequence andplaced in the outer packaging foil, with a liquid injection port beingleft. The electrolyte was injected via the liquid injection port,encapsulated, formed and capacity graded to obtain a lithium ionbattery. The fresh battery herein refers to a battery which is obtainedthrough aforementioned preparation process and is ready for shipping.

2. Test Methods of Battery Performance

(1) Test Method for Change in DC Internal Resistance at 20% SOC

At 25° C., the battery was charged to 4.45 V at a constant current of 1C (nominal capacity) and then charged to a current of ≤0.05 C at aconstant voltage of 4.45 V, allowed to stand for 5 min, and dischargedto a cut-off voltage of 3 V at a constant current of 1 C. The actualdischarge capacity was recorded. The battery was adjusted to 50% of thefull charge capacity required with the actual capacity, continuouslydischarged for 10 s at a current of 0.3 C. The DC internal resistances(DCIRs) (average of the measurements from 15 batteries) after one cycle,200 cycles and 400 cycles was obtained by dividing the current with thedifference between the voltage before discharge and the voltage at theend of discharge.

(2) Test Method for Storage Performance at High Temperature of 60° C.

The battery was allowed to stand at 25° C. for 30 minutes, charged to4.45 V at a constant current of 0.5 C and then charged to 0.05 C at aconstant voltage of 4.45 V, allowed to stand for 5 minutes, and thenstored at 60° C. for 21 days. The thickness expansion rate of thebattery was measured and calculated by a formula below:Thickness expansion rate=[(Thickness after storage−Thickness beforestorage)/Thickness before storage]×100%

(3) Test Method for Battery Capacity Retention Rate

At 45° C., the battery was charged to 4.45 V at a constant current of 1C and then charged to a current of 0.05 C at a constant voltage, anddischarged to 3.0 V at a constant current of 1 C, the above being thefirst cycle. Multiple cycles were performed on the battery under theabove conditions. The capacity retention rate of the fresh battery andthe battery after 200 cycles and 400 cycles was calculated respectively.The capacity retention rate after cycles is calculated by a formulabelow:Capacity retention rate after the cycle=(Discharge capacity aftercorresponding cycles/Discharge capacity after the first cycle)×100%

(4) Test Method for Voltage Drop

At 25° C., the battery was charged to 4.45 V at a constant current of 1C and then charged to a current of 0.05 C at a constant voltage,discharged to 3.2 V at a constant current of 1 C, and allowed to standfor 5 minutes. Then the voltage was tested, and after 24 h's storage at85° C., the voltage was tested again. Voltage drop=Voltage beforestorage−Voltage after storage.

(5) Intermittent Cycle Test Method

At 50° C., the lithium ion battery was charged to 4.45 V at a constantvoltage of 0.5 C and then to a cut-off current of 0.05 C at a constantcurrent, allowed to stand for 20 h and then discharged to 3.0 V at aconstant current of 0.5 C. Repeating charge/discharge as above, thecapacity retention rate of the fresh battery, and the battery after 30,50, and 100 cycles was calculated respectively. Capacity retention rateafter cycles=(Discharge capacity after corresponding cycles/Dischargecapacity of the first cycle)×100%

3. Test Results

The abbreviations for the chemical materials used in the examples ofresent application are shown in the following two tables:

Abbrevi- Abbrevi- Material ation Material Name ation Ethylene EC1,3-propanesultone PS carbonate Propylene PC Ethylene sulfate DTDcarbonate Ethyl methyl EMC Butanedinitrile SN carbonate Dimethyl DMCAdiponitrile ADN carbonate 1,4-dicyano-2-butene DCB Diethyl DEC1,3,6-Hexanetricarbonitrile HTCN-1 carbonate γ-butyrolactone GBL1,2,6-Hexanetricarbonitrile HTCN-2 γ-valerolactone VL1,3,5-Pentanetricarbonitrile PTCN Ethyl propionate EP Ethylene glycolbis(2-cyanoethyl) ether EDN Propyl PP1,1-difluoro-2,2-difluoroethyl-2′,2′difluoro- FEPE propionate3′,3′-difluoropropylether 2-trifluoromethyl-3-methoxyperfluoropentaneTMMP 2-(trifluoro-2-fluoro-3-difluoro)-3-difluoro-4- TPTPfluoro-5-trifluoropentane Vinylene VC 1-Propylphosphonic cyclicanhydride T3P carbonate Fluoroethylene FEC 1-Methylphosphonic cyclicanhydride TM3P carbonate 1-Ethylphosphonic cyclic anhydride TE3P1,2,3-tris(2-cyanoethoxy)propane TCEP

Dinitrile compound A A₁: SN; A₂: ADN; A₃: EDN; A₄: DCB Trinitrile B B₁:HTCN-1; B₂: HTCN-2; compound B₃: PTCN; B₄: TCEP Propyl propionate C (PP)Fluoroether D D₁: FEPE; D₂: TMMP; D₃: TPTP Cyclic phosphonic E E₁: T3PE₂: TM3P; E₃: TE3P anhydride Other additives F F₁: VC; F₂: PS; F₃: DTDCyclic carboxylate H H₁: GBL; H₂: VL ester Single- and double- G sidecompaction density

(1) Different amounts of a compound comprising two cyano groups, acompound comprising three cyano groups and/or propyl propionate as shownin Tables 1-1 and 1-2 were added to the basic electrolyte. Theelectrolyte was injected into a battery prepared according to the abovemethod. The DC internal resistance at 20% SOC of the batteries wastested. The test results are shown in Tables 1-1 and 1-2.

TABLE 1-1 DC internal resistance (mΩ) at 20% SOC A₁ B₁ C Fresh After 200After 400 (X wt %) (Y wt %) (Z wt %) X + Y X/Y Battery cycles cyclesS1-1 4 1 30 5 4 50.8 84.3 91.2 S1-2 4 2 30 6 2 54.4 88.0 98.6 S1-3 4 330 7 1.3 55.7 88.9 99.4 S1-4 4 0.5 30 4.5 8 57.8 92.0 101.0 S1-5 3 0.530 3.5 6 57.1 91.2 93.5 S1-6 4 0.4 30 4.2 10 55.9 99.4 112.8 S1-7 3 2 305 1.5 52.3 84.4 91.5 S1-8 2 2 30 4 1 51.9 84.2 91.4 S1-9 1 2 30 3 0.552.3 86.5 92.4 S1-10 0.5 2 30 2.5 0.25 54.8 79.4 102.5 S1-11 0.2 2 302.2 0.1 59.2 91.8 105.3 S1-12 1 5 30 6 0.2 58.5 97.0 104.1 S1-13 7 3 3010 2.3 60.4 92.9 107.3 D1-1 0 0 0 0 0 63.8 140.9 190.4 D1-2 0 1 0 1 062.3 138.5 188.2 D1-3 4 0 0 4 0 61.8 136.5 184.2 D1-4 0.1 1 0 1.1 0.163.8 120.9 126.4 D1-5 4 0.1 0 4.1 40 68.3 109.8 124.9 D1-6 7 5 0 12 1.469.2 112.3 133.0 D1-7 1 11 0 12 0.09 63.8 100.9 139.3 D1-8 11 1 0 12 1072.0 116.3 135.4

TABLE 1-2 DC internal resistance (mΩ) at 20% SOC A B C Fresh After 200After 400 (X wt %) (Y wt %) (Z wt %) X + Y X/Y Battery cycles cyclesS1-14 A₂ (4) B₂ (3) 30 7 1.3 55.5 88.1 98.7 S1-15 A₂ (4) B₂ (0.5) 30 4.58 57.2 91.6 100.6 S1-16 A₂ (3) B₂ (0.5) 30 3.5 6 55.9 89.4 98.8 S1-17 A₃(3) B₃ (2) 30 5 1.5 51.1 82.6 90.7 S1-18 A₃ (2) B₃ (2) 30 4 1 51.2 83.390.5 S1-19 A₃ (1) B₃ (2) 30 3 0.5 51.3 85.1 91.1 S1-20 A₃ (0.5) B₄ (2)30 2.5 0.25 54.3 79.1 90.1 S1-21 A₂ (0.2) B₂ (2) 30 2.2 0.1 58.5 91.2104.8 S1-22 A₂ (1) B₂ (5) 30 6 0.2 58.1 96.5 103.3 S1-23 A₂ (7) B₂ (3)30 10 2.3 60.2 92.3 106.5 S1-24 A₄ (2) B₃ (2) 30 4 1 57.9 86.1 93.4

As shown in Table 1-1, in Comparative Examples D1-1 to D1-8,butanedinitrile or 1,3,6-hexanetricarbonitrile was added alone, and nopropyl propionate was added. The DC internal resistance of the batterywas significantly increased after cycles.

When butanedinitrile, 1,3,6-hexanetricarbonitrile and propyl propionatewere used in Examples S1-1 to S1-13 simultaneously, the increase in DCinternal resistance of the battery after cycles was obviously inhibited.

When the propyl propionate content is kept unchanged, and the relationbetween the butanedinitrile content X and the1,3,6-hexanetricarbonitrile content Y is adjusted, it is found that whenX and Y meet the conditions represented by both Formula (1) and Formula(2): {about 2 wt %≤(X+Y)≤about 11 wt % . . . (1); and about0.1≤(X/Y)≤about 8 . . . (2)}, the inhibition effect on the increase inDC internal resistance of the battery after cycles is remarkable. When Xand Y meet about 2 wt %≤(X+Y)≤about 8 wt % and about 0.1≤(X/Y)≤about 6,the combination of the additives can exhibit synergistic effect and cansufficiently suppress the increase in DC internal resistance.

FIG. 1A shows the DC internal resistances of fresh batteries of ExamplesS1-1 and S1-2 of the present application and Comparative Example D1-1 atdifferent charge states (10% SOC, 20% SOC, and 70% SOC). FIG. 1B showsthe DC internal resistances of batteries of Examples S1-1 and S1-2 ofthe present application and Comparative Example D1-1 at different chargestates (10% SOC, 20% SOC, and 70% SOC) after 200 cycles of charge anddischarge. FIG. 1C shows the DC internal resistances of batteries ofExamples S1-1 and S1-2 of the present application and ComparativeExample D1-1 at different charge states (10% SOC, 20% SOC, and 70% SOC)after 400 cycles of charge and discharge. It can be seen that theincrease in DC internal resistance during cycles in Examples S1-1 andS1-2 is significantly improved compared with Comparative Example D1-1.

As shown in Table 1-2, when the dinitrile compound is adiponitrile orethylene glycol bis(2-cyanoethyl)ether, and the trinitrile compound is1,2,6-hexanetricarbonitrile, 1,3,6-Hexanetricarbonitrile, or1,2,3-tris(2-cyanoethoxy)propane, the effect of inhibiting the increasein DC internal resistance can also be achieved. When the dinitrilecompound is ethylene glycol bis(2-cyanoethyl)ether, or the trinitrilecompound is 1,2,3-tris(2-cyanoethoxy)propane, the effect of inhibitingthe increase in DC internal resistance of the battery after cycles ismore significant.

(2) Different amounts of a compound comprising two cyano groups, acompound comprising three cyano groups and/or propyl propionate as shownin Table 2 were added to the basic electrolyte. The electrolyte wasinjected into a battery prepared according to the above method. The DCinternal resistance at 20% SOC of the battery was tested. The testresults are shown in Table 2.

TABLE 2 DC internal resistance (mΩ) at 20% SOC C A₁ B₁ Fresh After 200After 400 (Z wt %) (X wt %) (Y wt %) Y/Z battery cycles cycles S1-1 30 41 0.03 50.8 84.3 91.2 S2-1 5 4 1 0.2 68.7 85.2 97.6 S2-2 10 4 1 0.1 60.383.1 95.7 S2-3 20 4 1 0.05 56.1 81.6 93.9 S2-4 40 4 1 0.025 47.5 78.287.2 S2-5 50 4 1 0.02 56.3 82.6 98.3 S2-6 10 4 3 0.3 64.3 89.5 97.7 S2-750 4 0.5 0.01 53.2 84.3 94.1 D2-1 4 4 1 0.25 72.1 108.5 118.9 D2-2 60 41 0.017 42.0 100.1 113.9 D2-3 10 4 5 0.5 62.3 85.4 111.3 D2-4 50 4 0.10.0025 53.2 89.3 109.4

As shown in Table 2, when the content of propyl propionate is within therange of 5 wt % to 50 wt %, the DC internal resistance of the freshbattery decreases continuously with the propyl propionate contentincreasing. In addition, when the content of the propyl propionate isless than 5 wt % or greater than 50 wt %, the DC internal resistance ofthe battery is greatly increased after 200 cycles, and the performanceis deteriorated. The combination of additives can form a cathodeprotection film so as to reduce the side reactions, thereby effectivelycontrolling the polarization and side reactions of the battery. Theratio of the content of the trinitrile compound to the content of propylpropionate has great effect on the change in DC internal resistance ofthe battery. When Y/Z is within the range of 0.01-0.3, a betterinhibition effect on the increase in DC internal resistance is achieved.

(3) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) and afluoroether of different contents as shown in Table 3 were added. Theobtained electrolyte was injected to a battery prepared according to theabove method. The DC internal resistance at 20% SOC and the 21-daythickness expansion rate at 60° C. were tested. The test results areshown in Table 3.

TABLE 3 DC internal resistance (mΩ) 21-day thickness D of fresh batteryexpansion rate at (content, wt %) at 20% SOC 60° C. S1-1 0 50.8 7.6%S3-1 D₁ (0.1) 50.2 6.2% S3-2 D₁ (0.5) 49.8 6.0% S3-3 D₁ (1) 48.6 5.7%S3-4 D₁ (1.5) 48.5 5.1% S3-5 D₁ (2) 48.4 4.8% S3-6 D₁ (2.5) 48.3 4.9%S3-7 D₁ (3) 48.1 5.6% S3-8 D₁ (5) 49.3 6.89% S3-9 D₂ (1) 49.2 6.1% S3-10D₃ (1) 49.4 5.7% D3-1 D₁ (6) 51.3 8.5%

As can be seen from Table 3, with the addition of fluoroether (0.1-5 wt%), the DC internal resistance and the thickness expansion rate of thefresh battery are improved to a certain extent, and the storageperformance is slightly decreased when the addition amount is large, butit is still within the desired range. When the fluoroether content ismore than 5 wt %, the DC internal resistance and the thickness expansionrate after storage at 60° C. of the fresh battery are deteriorated.

(4) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) and acyclic phosphonic anhydride of different contents as shown in Table 4were added. The obtained electrolyte was injected to a battery preparedaccording to the above method. The DC internal resistance at 20% SOC andthe capacity retention ratio of the battery were tested. The testresults are shown in Table 4.

TABLE 4 DC internal resistance (mΩ) at 20% SOC Capacity retention rate EFresh After 200 After 400 Fresh After 200 After 400 (content, wt %)battery cycles cycles battery cycles cycles S1-1 0 50.8 84.3 91.2 100%93.5% 86.3% S4-1 E₁ (0.1) 48.3 51.5 88.2 100% 95.7% 90.1% S4-2 E₁ (0.5)45.4 48.2 82.3 100% 96.3% 91.4% S4-3 E₁ (1) 44.6 47.1 80.5 100% 96.1%90.7% S4-4 E₁ (2) 45.6 47.3 81.6 100% 95.2% 89.6% S4-5 E₁ (3) 45.9 49.189.4 100% 94.7% 88.5% S4-6 E₂ (1) 45.2 48.3 88.3 100% 95.3% 91.0% S4-7E₃ (1) 45.3 48.7 89.5 100% 95.1% 90.8% D4-1 E₁ (4) 46.1 58.6 105.3 100%92.1% 85.3%

It can be seen from Table 4 that with the addition of cyclic phosphonicanhydride (0.1-3 wt %), the DC internal resistance of the fresh batteryand the battery after cycles is improved to a certain extent, which maybe attributed to the relatively stable structure of the compositeprotective film formed by the combined additives; and the cycleperformance is improved first and then deteriorated with the addition ofthe cyclic phosphonic anhydride. When the content is more than 3 wt %,the cycle performance is affected, which may be caused by thedecomposition of the cyclic phosphonic anhydride.

(5) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetrinitrile (B1) and afluoroether and a cyclic phosphonic anhydride of different contents asshown in Table 5 were added. The obtained electrolyte was injected to abattery prepared according to the above method. The DC internalresistance at 20% SOC, the 21-day thickness expansion rate at 60° C.,and the capacity retention rate of the battery were tested. The testresults are shown in Table 5.

TABLE 5 21-day DC internal resistance thickness D₁ E₁ (mΩ) at 20% SOCexpansion Capacity retention rate (content: (content: Fresh After 200After 400 rate at Fresh After 200 After 400 wt %) wt %) battery cyclescycles 60° C. battery cycles cycles S1-1 0 0 50.8 84.3 91.2 7.6% 100%93.5% 86.3% S3-1 0.1 0 50.2 83.1 90.4 6.2% 100% 94.2% 87.9% S4-2 0 0.545.4 48.2 82.3 6.7% 100% 96.3% 91.4% S5-1 0.1 0.5 44.7 47.2 80.8 6.0%100% 96.4% 91.6% S5-2 1 0.5 43.8 46.3 80.5 5.3% 100% 96.8% 91.7% S5-3 10.3 44.1 48.2 79.3 4.3% 100% 97.1% 92.3% S5-4 1 0.1 46.3 50.5 86.2 4.5%100% 97.6% 92.9% S5-5 3 2 43.5 47.1 81.3 4.0% 100% 94.8% 89.4%

As can be seen from Table 5, with the addition of the fluoroether andthe cyclic phosphonic anhydride, the DC internal resistance, the storageperformance and the cycle performance of the fresh battery and thebattery after cycles are further improved.

(6) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) andother additives of different contents as shown in Table 6 were added.The obtained electrolyte was injected to a battery prepared according tothe above method. The voltage drop after storage at 3.2V and 85° C. for24 h of the battery were tested. The test results are shown in Table 6.

TABLE 6 VC VEC FEC PS DTD Voltage drop after (content: (content:(content: (content: (content: storage at 3.2 V and wt %) wt %) wt %) wt%) wt %) 85 C. for 24 hrs S6-1 0.5 — — — — 0.35 V S6-2 0.5 — — 3 — 0.32V S6-3 0.5 — — 3 0.5 0.23 V S6-4 1 — — 3 —  0.3 V S6-5 1 — 3 3 — 0.20 VS6-6 — 0.5 — 3 0.5 0.25 V D6-1 — — — — —  0.4 V

The addition of the film-forming additives VC, VEC, FEC, PS, DTD canfurther improve the stability of the solid electrolytic interface (SEI)film of the battery. Using a combination of various additives is moreconducive to improve the stability of the battery, which is beneficialto the long-term storage of the battery and thus improves the batteryreliability.

(7) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) wereadded. The obtained electrolyte was injected to a battery preparedaccording to the above method. The electrode compaction density ratio(D1/D2) of the battery was changed according to Table 7, and thecapacity retention rate of the battery was tested. The test results areshown in Table 7.

TABLE 7 Capacity retention rate Compaction density Fresh After 200 After400 ratio (D1/D2) battery cycles cycles S7-1 0.8 100% 93.8% 89.3% S7-20.9 100% 95.3% 90.1% S7-3 0.95 100% 95.9% 90.8% S7-4 1.0 100% 96.8%91.4% S7-5 1.05 100% 95.8% 90.7% S7-6 1.1 100% 95.2% 90.2% S7-7 1.2 100%93.7% 88.8% D7-1 1.3 100% 91.2% 83.6% D7-1 0.7 100% 90.5% 82.7%

As can be seen from Table 7, the electrode compaction density ratio(D1/D2) of the lithium ion battery has a significant effect on the cycleperformance of the lithium ion battery. A too large or too small D1/D2will damage the cycle performance of lithium-ion batteries. It can beseen that when D1/D2 is within the range of 0.8-1.2, a better cycleperformance is obtained, possibly because the combined additivesfacilitate the reduction of the electrode interface resistance and thereduction of the cell polarization.

(8) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) and acyclic phosphonic anhydride of different contents as shown in Table 8were added. The obtained electrolyte was injected to a battery preparedaccording to the above method. The electrode compaction density ratio(D1/D2) was changed according to Table 8, and the capacity retentionrate of the obtained battery was tested. The test results are shown inTable 8.

TABLE 8 Capacity retention rate D₁ E₁ Fresh After 200 After 400(content:) (content:) G battery cycles cycles S8-1 1 — 0.8 100% 94.9%90.1% S8-2 1 — 1.0 100% 97.3% 92.5% S8-3 1 — 1.2 100% 94.8% 89.9% S8-4 —0.3 0.8 100% 94.3% 89.6% S85 — 0.3 1.0 100% 97.9% 92.2% S8-6 — 0.3 1.2100% 95.0% 90.5% S8-7 1 0.3 1.0 100% 98.1% 93.3%

With the addition of the fluoroether or the cyclic phosphonic anhydride,the cycle performance of the lithium ion battery is further improvedwhen the electrode compaction density of the battery is within the rangeof 0.8-1.2.

(9) To the basic electrolyte, 30 wt % of propyl propionate, 4 wt % ofbutanedinitrile (A1), 1 wt % of 1,3,6-hexanetricarbonitrile (B1) and acyclic carboxylate ester of different contents as shown in Table 9 wereadded.

The obtained electrolyte was injected to a battery prepared according tothe above method. The capacity retention rate after intermittent cycleof the obtained battery was tested. The test results are shown in Table9.

TABLE 9 Capacity retention rate after intermittent cycle H Fresh After30 After 50 After 100 (content: wt %) battery cycles cycles cycles S1-10 100% 73.80% 64.30% 54.50% S9-1 H₁ (1) 100% 82.50% 74.60% 64.20% S9-2H₁ (10) 100% 87.20% 81.40% 77.20% S9-3 H₁ (20) 100% 86.20% 81.30% 78.00%S9-4 H₁ (30) 100% 88.30% 83.30% 79.80% S9-5 H₁ (40) 100% 87.50% 80.60%75.20% S9-6 H₁ (50) 100% 86.30% 74.40% 63.20% S9-7 H₁ (60) 100% 85.20%71.60% 57.60% S9-8 H₂ (1) 100% 81.80% 73.20% 61.80% S9-9 H₂ (10) 100%86.50% 80.80% 76.10% S9-10 H₂ (20) 100% 85.30% 81.30% 77.10% S9-11 H₂(30) 100% 88.10% 83.00% 79.30% S9-12 H₂ (40) 100% 87.10% 80.10% 74.80%S9-13 H₂ (50) 100% 85.20% 73.70% 61.90% S9-14 H₂ (60) 100% 82.20% 70.10%55.90%

The capacity retention rate after intermittent cycle of the batteryincreases with the increase of the amount of the cyclic carboxylateester, possibly because the cyclic carboxylate forms a passivated filmon the surface of the cathode. However, when the cyclic carboxylateester content is close to 40 wt %, the intermittent cycle performancedeteriorates to a certain extent, which is mainly caused by a sidereaction between LiPF₆ and the cyclic carboxylate ester. Therefore, theamount of the cyclic carboxylate ester is preferably moderate and shouldnot be too large.

References throughout the specification to “some embodiments”, “partialembodiments”, “one embodiment”, “another example”, “example”, “specificexample” or “partial examples” mean that at least one embodiment orexample of the application includes specific features, structures,materials or characteristics described in the embodiments or examples.Thus, the descriptions appear throughout the specification, such as “insome embodiments”, “in an embodiment”, “in one embodiment”, “in anotherexample”, “in an example”, “in a particular example” or “for example”,are not necessarily the same embodiment or example in the application.Furthermore, the particular features, structures, materials orcharacteristics herein may be combined in any suitable manner in one ormore embodiments or examples.

While the illustrative embodiments have been shown and described, itwill be understood by those skilled in the art that the embodiments arenot to be construed as limiting the present invention, andmodifications, substitutions and changes can be made to the embodimentswithout departing from the spirit and scope of the present application.

The above-described embodiments of the present invention are intended tobe illustrative only. Numerous alternative embodiments may be devised bypersons skilled in the art without departing from the scope of thefollowing to claims.

What is claimed is:
 1. An electrolyte, comprising a dinitrile compound,a trinitrile compound, and propyl propionate, wherein, based on a weightof the electrolyte, a weight percentage of the dinitrile compound is X,a weight percentage of the trinitrile compound is Y, and a weightpercentage of the propyl propionate is Z; wherein, about 2 wt%≤(X+Y)≤about 8 wt %, about 0.1≤(X/Y)≤about 6, and about0.01≤(Y/Z)≤about 0.3; wherein the dinitrile compound comprises acompound of Formula (5):CN—R₂—(O—R₃)_(n)—O—R₄—CN  (5); where R₂, R₃ and R₄ are eachindependently an alkylene group having 1-5 carbon atoms or an alkenylenegroup having 2-5 carbon atoms, and n represents an integer from 0 to 5;wherein the trinitrile compound is one selected from the groupconsisting of: 1,3,5-pentanetricarbonitrile; 1,2,3-propanetrinitrile;1,3,6-hexanetricarbonitrile; 1,2,6-hexanetricarbonitrile;1,2,3-tris(2-cyanoethoxy)propane; 1,2,4-tris(2-cyanoethoxy)butane;1,1,1-tris(cyanoethoxymethylene)ethane;1,1,1-tris(cyanoethoxymethylene)propane;3-methyl-1,3,5-tris(cyanoethoxy)pentane; 1,2,7-tris(cyanoethoxy)heptane;1,2,6-tris(cyanoethoxy)hexane; 1,2,5-tris(cyanoethoxy)pentane; and anycombination thereof.
 2. The electrolyte according to claim 1, whereinthe dinitrile compound is one selected from the group consisting ofethylene glycol bis(2-cyanoethyl)ether, diethylene glycolbis(2-cyanoethyl)ether, triethylene glycol bis(2-cyanoethyl)ether,tetraethylene glycol bis(2-cyanoethyl)ether,3,6,9,12,15,18-hexaoxaeicosanoic dinitrile,1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane,1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl)ether,and any combination thereof.
 3. The electrolyte according to claim 1,wherein the dinitrile compound further comprises a compound of Formula(4):CN—R₁—CN  (4); where R₁ selected from an alkylene group having 1-5carbon atoms or an alkenylene group having 2-5 carbon atoms.
 4. Theelectrolyte according to claim 3, wherein the dinitrile compoundrepresented by Formula (4) is one selected from the group consisting ofbutanedinitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane,1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane,1,9-dicyanononane, 1,10-dicyanodecane, 1,12-dicyanododecane,tetramethylbutanedinitrile, 2-methylglutaronitrile,2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile,1,4-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanooctane,2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene,1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,5-dioxa-pimelonitrile,1,4-bis(cyanoethoxy)butane, 1,4-dicyano-2-butene,1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene,1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene,1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene,1,6-dicyano-2-methyl-5-methyl-3-hexene, and any combination thereof. 5.The electrolyte according to claim 1, wherein the trinitrile compoundcomprises a compound of Formula (6), (7) or a combination thereof:

where in Formula (6), x, y, and z represent an integer from 0 to 5, andx, y, and z are not 0 at the same time; and in Formula (7), R₅represents hydrogen or an alkyl group having 1-5 carbon atoms, R₆, R₇and R₈ are each independently an alkylene group having 1-5 carbon atoms,and X₄, X₅ and X₆ are each independently —R₉—CN, in which R₉ representsan alkylene group having 1-5 carbon atoms.
 6. The electrolyte accordingto claim 1, wherein X is about 0.01-10 wt %, Y is about 0.01-10 wt %,and a weight percentage Z of the propyl propionate is about 5-50 wt %.7. The electrolyte according to claim 1, further comprising afluoroether comprising at least one of the compounds of Formula (8),Formula (9), Formula (10) or Formula (11):Rf1-O—Rf2  (8);Rf1-O—R  (9)Rf1-O—(R′—O)_(n)—Rf2  (10); andRf1-O—(R′—O)_(n)—R  (11); wherein Formulae (8), (9), (10), and (11), Rf1and Rf2 are each independently a linear or branched C₁ to C₁₂fluoroalkyl group having at least one hydrogen atom substituted withfluoro, R is a linear or branched C₁ to C₁₂ alkyl group, and R′ is alinear or branched C₁ to C₅ alkylene group, and n is an integer from 1to
 5. 8. The electrolyte according to claim 7, wherein Rf1 or Rf2 iseach independently a fluoroalkyl group selected from the groupconsisting of HCF₂—, CF₃—, HCF₂CF₂—, CH₃CF₂—, CF₃CH₂—, CF₃CF₂—,(CF₃)₂CH—, HCF₂CF₂CH₂—, CF₃CH₂CH₂—, HCF₂CF₂CF₂CH₂—, HCF₂CF₂CF₂CF₂CH₂—,CF₃CF₂CH₂—, CF₃CFHCF₂CH₂—, HCF₂CF(CF₃)CH₂—, and CF₃CF₂CH₂CH₂—.
 9. Theelectrolyte according to claim 7, wherein the fluoroether is oneselected from the group consisting of: HCF₂CF₂CH₂OCF₂CF₂H,(CF₃)₂CFCF(CF₂CF₃)(OCH₃), CF₃CHFCF₂CH(CH₃)OCF₂CHFCF₃,HCF₂CF₂CH₂OCF₂CF₂CF₂CF₂H, HCF₂CF₂OCH₂CF₃, HCF₂CF₂OCH₂CH₂OCF₂CF₂H,HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂H, HCF₂CF₂CH₂OCF₂CF₂CF₂H,HCF₂CF₂OCH₂CH₂OCF₂CF₂CF₂H, HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂H,CH₃OCH₂CH₂OCH₂CH₂F, CH₃OCH₂CH₂OCH₂CF₃, CH₃OCH₂CH(CH₃)OCH₂CH₂F,CH₃OCH₂CH(CH₃)OCH₂CF₃, FCH₂CH₂OCH₂CH₂OCH₂CH₂F,FCH₂CH₂OCH₂CH(CH₃)OCH₂CH₂F, CF₃CH₂O(CH₂CH₂O)₂CH₂CF₃,CF₃CH₂OCH₂CH(CH₃)OCH₂CF₃, and any combination thereof.
 10. Theelectrolyte according to claim 1, further comprising a cyclic phosphonicanhydride, based on the weight of the electrolyte, a content of cyclicphosphonic anhydride is about 0.01-10 wt %.
 11. The electrolyteaccording to claim 1, further comprising one selected from the groupconsisting of: a cyclic carbonate ester having a carbon-carbon doublebond, a fluorinated chain carbonate ester, a fluorinated cycliccarbonate ester, a compound having a sulfur-oxygen double bond, and anycombination thereof.
 12. The electrolyte according to claim 1, furthercomprising a cyclic carboxylate ester, including γ-butyrolactone orγ-valerolactone or a combination thereof.
 13. An electrochemical device,comprising: an electrode; and an electrolyte comprising a dinitrilecompound, a trinitrile compound, and propyl propionate, wherein, basedon a weight of the electrolyte, a weight percentage of the dinitrilecompound is X, a weight percentage of the trinitrile compound is Y, anda weight percentage of the propyl propionate is Z; wherein, about 2 wt%≤(X+Y)≤about 8 wt %, about 0.1≤(X/Y)≤about 6, and about0.01≤(Y/Z)≤about 0.3; wherein the dinitrile compound comprises acompound of Formula (5):CN—R₂—(O—R₃)_(n)—O—R₄—CN  (5); where R₂, R₃ and R₄ are eachindependently an alkylene group having 1-5 carbon atoms or an alkenylenegroup having 2-5 carbon atoms, and n represents an integer from 0 to 5wherein the trinitrile compound is one selected from the groupconsisting of: 1,3,5-pentanetricarbonitrile; 1,2,3-propanetrinitrile;1,3,6-hexanetricarbonitrile; 1,2,6-hexanetricarbonitrile;1,2,3-tris(2-cyanoethoxy)propane; 1,2,4-tris(2-cyanoethoxy)butane;1,1,1-tris(cyanoethoxymethylene)ethane;1,1,1-tris(cyanoethoxymethylene)propane;3-methyl-1,3,5-tris(cyanoethoxy)pentane; 1,2,7-tris(cyanoethoxy)heptane;1,2,6-tris(cyanoethoxy)hexane; 1,2,5-tris(cyanoethoxy)pentane; and anycombination thereof.
 14. The electrolyte according to claim 1, whereinthe initrile compound comprises a compound of Formula (5):CN—R₂—(O—R₃)_(n)—O—R₄—CN  (5); where R₂, R₃ and R₄ are eachindependently an alkylene group having 1-5 carbon atoms or an alkenylenegroup having 2-5 carbon atoms, and n represents an integer from 2 to 5.15. The electrochemical device according to claim 13, wherein theelectrode comprising: a current collector, a single-sided coating and adouble-sided coating; a first part of the current collector has thesingle-sided coating and a second part of the current collector has thedouble-sided coating; and an electrode compaction density of theelectrode corresponding to the first part having the single-sidedcoating is D1, and, an electrode compaction density of the electrodecorresponding to the second part having the double-sided coating is D2,wherein, about 0.8≤D1/D2≤about 1.2.
 16. The electrochemical deviceaccording to claim 15, wherein, the electrode is a cathode, and 3.5g/cm³≤D2≤4.3 g/cm³; or, the electrode is an anode, and 1.2 g/cm³≤D2≤1.8g/cm³.
 17. An electrochemical device, comprising: electrodes; and anelectrolyte comprising a dinitrile compound, a trinitrile compound, andpropyl propionate, wherein, based on a weight of the electrolyte, aweight percentage of the dinitrile compound is X, a weight percentage ofthe trinitrile compound is Y, and a weight percentage of the propylpropionate is Z; wherein, about 2 wt %≤(X+Y)≤about 8 wt %, about0.1≤(X/Y)≤about 6, and about 0.01≤(Y/Z)≤about 0.3; wherein the dinitrilecompound comprises a compound of Formula (5):CN—R₂—(O—R₃)_(n)—O—R₄—CN  (5); where R₂, R₃ and R₄ are eachindependently an alkylene group having 1-5 carbon atoms or an alkenylenegroup having 2-5 carbon atoms, and n represents an integer from 0 to 5wherein the trinitrile compound is one selected from the groupconsisting of: 1,3,5-pentanetricarbonitrile; 1,2,3-propanetrinitrile;1,3,6-hexanetricarbonitrile; 1,2,6-hexanetricarbonitrile;1,2,3-tris(2-cyanoethoxy)propane; 1,2,4-tris(2-cyanoethoxy)butane;1,1,1-tris(cyanoethoxymethylene)ethane;1,1,1-tris(cyanoethoxymethylene)propane;3-methyl-1,3,5-tris(cyanoethoxy)pentane; 1,2,7-tris(cyanoethoxy)heptane;1,2,6-tris(cyanoethoxy)hexane; 1,2,5-tris(cyanoethoxy)pentane; and anycombination thereof.
 18. The electrochemical device according to claim17, wherein the electrodes comprising: a first electrode and a secondelectrode; where the first electrode comprises a first current collectorand a single-sided coating; the second electrode comprises a secondcurrent collector and a double-sided coating; and an electrodecompaction density of the first electrode comprising the single-sidedcoating is D1, and, an electrode compaction density of the secondelectrode comprising the double-sided coating is D2, wherein, about0.8≤D1/D2≤about 1.2.
 19. The electrochemical device according to claim17, wherein, the first electrode is a cathode, the second electrode is acathode, and 3.5 g/cm³≤D2≤4.3 g/cm³; or, the first electrode is ananode, the second electrode is an anode, and 1.2 g/cm³≤D2≤1.8 g/cm³.